The major goals of this research project are: (1) to study the protein structure of various murine thymus-leukemia antigens (TLA), (2) to analyze the differentiation pathways and immune functional properties of T cells that are derived from TLA plus or TLA minus thymocytes (of TLA plus mouse strains), and (3) to prepare murine fused cell hybrids and clone anti-TLA secreting hybridomas. These studies will attempt to compare and contrast the major structural and biological properties of TLA with the antigens of the major histocompatibility complex (MHC). The principal methods used in these studies will be radioisotope labeling of cell membrane antigens, immunospecific isolation and polyacrylamide gel electrophoresis of labeled TLA and MHC antigens. Proteolytic cleavage, acid cleavage and peptide mapping will also be used to characterize and compare the TLA associated with different Tla haplotypes. Thymocyte transfers between TLA-congenic mouse strains will be used to study the differentiative potential of TLA plus and TLA minus thymocytes. TLA and MHC antigens are coded for by linked genes on the seventeenth chromosome. Their gross chemical structure is very similar and it is probable that each arose from a common ancestral gene. This genetic and protein structural evidence forms the basis for the assumption that these two classes of lymphocyte surface antigens have similar and related functions.